Multicomponent degradable materials and use

ABSTRACT

In general, the current disclosure relates to multicomponent fibers that have accelerated degradation in water in low temperature conditions, and their various industrial, medical and consumer product uses. Such materials are especially useful for uses in subterranean wells in oil and gas production. In some embodiments, the compositions of materials have accelerated degradation even at Ultra Low Temperature (“ULT”) (≦60° C.) in subterranean formations.

BACKGROUND

Degradable materials have many uses in our society, ranging from making degradable plastic bags, diapers, and water bottles, to making degradable excipients for drug delivery and degradable implants for surgical use, to a wide variety of industrial uses, such as in remediation, agriculture, and oil and gas production.

For example, degradable materials have been used for fluid loss control, for diversion, and as temporary plugs in downhole applications of oil and gas production. Examples of degradable materials used in such ways include rock salt, graded rock salt, benzoic acid flakes, wax beads, wax buttons, oil-soluble resin material, etc. In addition to filling and blocking fractures and permeable zones right in the reservoir, degradable materials have also been used to form consolidated plugs in wellbores that will degrade after use, eliminating the need for retrieval.

New materials that can be used in such applications are always needed, however, and in particular materials that degrade under downhole conditions are particularly needed.

SUMMARY

In general, the current disclosure relates to multicomponent fibers that have accelerated degradation in water in low temperature conditions, and their various industrial, medical and consumer product uses. Such materials are especially useful for uses in subterranean wells in oil and gas production. In some embodiments, the compositions of materials have accelerated degradation even at Ultra Low Temperature (“ULT”) (≦60° C.) in subterranean formations.

In some cases, the multicomponent fibers comprise components that degrade at different rates in water, or water soluble components in combination with water degradable components, or hydrocarbon soluble components in combination with water degradable components. Some of the multicomponent fibers described herein lost more than 60% weight at temperatures below 60° C. in water within a week.

The degradable materials described herein, especially the non-toxic materials, have a variety of uses, e.g., to make consumer products such as plastic grocery bags and diaper liners, and also medical uses as implants, bandages, sutures, or drug delivery materials. However, our main interest for such material lies in oil and gas production, and other geological, mining, agriculture or remediation uses.

Embodiments of the current application can be used in various operations servicing subterranean wells. For example, materials of the current application can be applied to proppant flowback control, transportation of proppant, diversion in hydraulic fracturing, carbonate acidizing, and flow channeling in proppant pack.

Materials of the current application can also be added to drilling fluids to help minimize lost circulation, and added to cement to improve the flexural strength of the set cement. In some of the applications, such as diversion and carbonate acidizing, materials of the current application (such as fibers) may form a temporary plug in a fracture, a perforation, a wellbore or more than one of the locations in a well to allow some downhole operations, and the plug then degrades or dissolves after a selected time, such that the plug disappears. The materials can even be formed into solid plugs for temporary uses to plug wellbore equipment.

The time frame for the fiber to degrade to remove the fiber plugs is dependent on the choice of fibers (polymers) and on wellbore temperatures. However, the materials of the invention degrade in water at 60° C. in less than a month. Degradation can be accelerated with additives, with reactive fillers or with acids or bases in the injection fluid.

According to certain embodiments of the current application, there are provided multicomponent composite fibers having components that degrade at different rates in water, or having water soluble components (sheath or core, sea or one side) in combination with water degradable components, or having hydrocarbon soluble component (core, island or one side) in combination with water degradable components.

In addition, such multicomponent fibers may be processable, have comparable strength and stiffness to mono-component PLA fibers, and contain locally concentrated reactive fillers and other additives that promote fast degradation in water at low temperatures (T≦60° C.) in subterranean wells.

Materials that are suitable for the current application include, but are not limited to, polymers that are capable of being degraded (break down to oligomers or monomers) in aqueous environment. The polymer degradation in water is measurable by the decrease of molecular weight of the polymer (measured by drying and weighing, or by gel permeation chromatography), and the weight loss of the solid polymers over a period of time from a few hours, to a few days, weeks and months depending on the temperatures, the pH of the water, the nature of the polymers and whether the presence of a catalyst. For a downhole application, degradation can also be assessed by permeability, such that the polymer degrades or solubilizes enough to allow fluid flow.

Examples of the suitable, degradable polymers for the degradable composites include, but are not limited to, aliphatic polyesters, poly(lactic acid), poly(ε-caprolactone), poly(glycolic acid) (PGA), poly(lactic-co-glycolic acid) (PLGA), poly(hydroxyl ester ether), poly(hydroxybutyrate), poly(anhydride), polycarbonate, poly(amino acid), poly(ethylene oxide), poly(phosphazene), polyether ester, polyester amide, polyamides, sulfonated polyesters, poly(ethylene adipate) (PEA), polyhydroxyalkanoate (PHA), poly(ethylene terephtalate) (PET), poly(butylene terephthalate) (PBT), Poly(trimethylene terephthalate) (PTT), poly(ethylene naphthalate) (PEN) and copolymers, blends, derivatives or combination of any of these degradable polymers.

In some cases, the degradable polymers are poly(lactic acids), poly(ε-caprolactones), poly(glycolic acids) (PGA), and poly(lactic-co-glycolic acids) (PLGA). Poly(lactic acids) can be produced either by direct condensation of lactic acids or by catalytic ring-opening polymerization of cyclic lactides, or can be commercially provided.

Lactic acid, often produced commercially through bacterial fermentation, is a chiral molecule and has two optical active isomers: the D isomer and the L isomer. The D isomer content in the PLA determines the crystallinity of the PLA polymer. Fully amorphous PLA incudes relatively high D content (>20%) where highly crystalline PLA contains less than 2% D isomer.

Examples of the amorphous PLA resins include 6060D, 6302D, or 4060D resins from Natureworks. Examples of crystalline PLA resins include 6201D or 6202D resins from Natureworks. The matrix polymer in the degradable composites may comprise only the amorphous, only the crystalline PLA, or the blend of amorphous and crystalline PLA. A PLA polymer blend can be a simple mechanical mixture of molten amorphous and crystalline PLA polymers.

In some embodiments, a reactive filler, such as a base, metal oxide, or other catalysts can be included inside the fibers to accelerate degradation through fast water diffusion and fast kinetics. Besides basic properties, the additives can provide metal ions (Zn²⁺, Mg²⁺, etc.) that may act as Lewis acids and enhance ester bond cleavage as well. Thus, such additives can assist in controlling the rate of degradation.

The reactive fillers may include, but are not limited to, bases or base precursors that generate hydroxide ions or other strong nucleophiles when in contact with water. The reactive fillers improve both the rate of water penetration into the fibers and the rate of ester hydrolysis through the catalytic effect of nucleophiles.

Examples of reactive fillers include, but are not limited to, Ca(OH)₂, Mg(OH)₂, CaCO₃, Borax, MgO, CaO, ZnO, NiO, CuO, Al₂O₃, and other bases or compounds that can convert to bases when in contact with water.

Taking advantage of this multicomponent fiber technology and carefully designed multicomponent composite fibers that allow reactive fillers to concentrate in certain part of the fibers may result in rapid degradation of the polymers surrounding the filler particles, and cause the fiber to deteriorate into small particles (particle size <20 um) within one or two weeks at ultra low temperatures (<60° C.).

If needed, the reactive fillers in the multicomponent fibers can be surrounded by another component of polymer. Thus, the fibers can be used in applications in both neutral and acid solution without undesired interference from the reactive fillers. In other embodiments, the fillers are contained on the outside and e.g., acid is used to accelerate degradation. In some embodiments, the reactive fillers are dispersed uniformly in at least one of the polymer components.

The concentration of the reactive fillers, defined as weight % of filler in one polymer component, may be the same (evenly distributed reactive fillers in the fibers) or may be different in each polymer component so that the reactive fillers are locally concentrated in certain parts of the fibers.

The materials of the current application may be in the shape of rods, particles, beads, films and fibers. Alternative, a solid plug or other shape can be formed, for example by pressing. Fabrics and woven mats can also be made with the fibers.

In some embodiments, multicomponent fibers are made from extruding two or more polymers from the same spinneret with both polymers contained within the same filament. By this technique, polymers with different properties can be tailored into the same filament with any desired cross sectional shapes or geometries. In the multicomponent fibers, two or more polymer components can be joined, combined, united or bonded to form a unitary fiber body.

Multicomponent fibers can be classified by their fiber cross-section structures as side-by-side, sheath-core, islands-in-the-sea and citrus fibers or segmented-pie cross-section types, and various combinations thereofIGS. 1 and 2 show the examples of cross sections of multicomponent fibers.

Polymer resins with different morphology, melting temperatures, dissolution and degradation kinetics may also be designed into multicomponent fibers to achieve the optimum degradation, tensile strength and dimension stability (minimum shrinkage) at given temperatures in water.

Fibers can also include other types of additives in addition to reactive fillers, for example to impart color, flexibility, or other desirable properties. The particle sizes of the various additives may be in the range of 10 nm to several hundred nanometers. Reactive fillers with larger total surface area may result in faster degradation at the given temperatures compared to bigger fillers with smaller total surface area.

The loading of the various fillers as a weight percentage of the total composite can be in the range of 0-10% or 0.2% to 4% in fibers, depending on the choice of fillers, their molecular weight and the process condition. Each filler can be used alone or combined with other fillers and additives. The most preferred fillers for developing degradable/soluble bicomponent fibers are ZnO and the combination of ZnO with a small amount of other fillers, such as MgO, salts, waxes, plasticizers, and hydrophilic polymers such as ethylene vinyl alcohol (EVOH) or polyvinyl alcohol (PVOH).

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise.

The term “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated.

The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive.

The terms “comprise”, “have”, “include” and “contain” (and their variants) are open-ended linking verbs and allow the addition of other elements when used in a claim.

The phrase “consisting of” is closed, and excludes all additional elements.

The phrase “consisting essentially of” excludes additional material elements, but allows the inclusions of non-material elements that do not substantially change the nature of the invention.

By “multicomponent fibers” what is meant is that a fiber has at least two different components therein, and such components are at least partially adjacent each other, although many configurations thereof are possible. The term does not include fibers where the components are intimately admixed or blended, however.

By “bicomponent fibers” what is meant is that a fiber has two different components therein that are adjacent.

By “degradable polymer” what is meant is a polymer that can be degraded in water at 60° C. in 30 days or less, preferably in two weeks, or a week or less.

By “degraded” what is meant is at least a 50% reduction in dry weight or if assessed downhole by flowthrough at least a 50% increase in flow.

By “hydrocarbon soluble polymer” what is meant is a polymer that is soluble in petroleum hydrocarbons in 30 days or less, preferably in two weeks or in a week or less.

By “water soluble polymer” what is meant is a polymer that dissolves in water in 30 days or less, preferably in two weeks or in a week or less.

The following abbreviations are used herein:

ABBREVIATION TERM DI Deionized water DMAP 4-Dimethylaminopyridine G-PVOH Nichigo G-polymer ™ PLA Polylactic acid SEM Scanning electron microscope ULT Ultra low temperatures

DESCRIPTION OF FIGURES

FIG. 1: Examples of sheath-core (1 and 2), islands-in-the-sea (3 and 4) and segmented-pie (5 and 6) cross-section types.

FIG. 2: Cross-section of various side-by-side multicomponent fibers.

FIG. 3. Schematic view of Fibers 1 in Table 1.

FIG. 4A-D. Schematic views of bicomponent fibers consisting of degradable polymer and water soluble polymer.

FIG. 5A-B. Schematic views of bicomponent fibers consisting of degradable polymer and oil soluble polymer.

FIG. 6A-B. The optical images of the bicomponent fibers. A: Bi-50S/50C—ZnO; B: Bi-75S/25C.

FIG. 7. The degradation of the bicomponent fibers, Bi-50S/50C (vertical hatching) and Bi-75S/25C (horizontal hatching) having different rations of core versus sheath material, at 60° C. in water over 14 or 21 days.

FIG. 8. The degradation profiles of the bicomponent fibers, Bi-50S/50C (star) and Bi-50S/50C—ZnO (4%) (circle), at 60° C. in water versus time in days.

FIG. 9. Influence of additives on the degradation rate of PLA fibers at 60° C. for 48 hours. The PLA fibers were provided by NatureWorks.

FIG. 10A-B. A: SEM image of as-spun PLA/G-PVOH (8042p) bicomponent fiber with a sheath:core ratio at 31%:69%. B: The optical image of the cross-section of the same PLA/G-PVOH sheath-core fiber.

FIG. 11. The degradation of the PLA/G-PVOH fibers in water and buffered solutions at varying pH versus time in days. Left panel, T=49° C., Right T=60° C.

FIG. 12A-B. SEM images of PLA/G-PVOH fibers after 7 days in deionized (DI) water at 49° C. (A) and 60° C. (B).

FIG. 13. Photograph of glass vials containing 0.25 g of Evatane® 28-05 (left) and Evatane® 28-40 (right) in 8 ml of octane. Both resins dissolved in octane at 38° C. after 5 hours.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited.

In the summary and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.

Different types of polymers or similar polymers with different crystallinity, melting point, degradation kinetics and solubility can be used to form the components in the multicomponent fibers. Depending on the final applications (such as, proppant transport or bridging and plugging), there are a variety of choices of configurations and compositions for multicomponent composite fibers, and the fiber body can have a variety of regular or irregular cross-sectional shapes.

For example, the polymer components can be arranged to form a core-sheath configurations shown as 1 and 2 cross section in FIG. 1, island-sea with up to 360 islands (3 and 4 cross section in FIG. 1), and segmented pie (4-64 segments) shown as 5 and 6 cross-section in FIG. 1.

FIG. 2 shows the examples of side-by-side multicomponent fibers comprising different polymers or similar polymers with different melting points, degradation kinetics and physical properties.

Combinations of the above configurations are also possible.

Each component of a multicomponent fiber may occupy 10-90% of the weight of the entire fiber, or 25-75%, or 50-50% or any range in between. The components can be regular or irregular in shape or cross-section, and components can be symmetrically or asymmetrically placed (e.g., a core can be off-center).

In all cases, the reactive filler can be in one component or the other, or in all components, as needed for degradation kinetics, strength and the actual application. Reactive fillers can comprise 0-10% or 0.2-4% of the component to which it is added. More can be used if needed for particular applications.

Poly(lactic acid) (PLA) with different crystallinity levels, as examples of degradable polyesters, are used to construct the multicomponent fibers. The selection of the PLA resin is based on their melting temperatures, the rate of water penetration, and the degradation kinetics, all of which correlate to the crystallinity of PLA polymers. For example, PLA with the melting point of 125-135° C. is an amorphous polymer that degrades faster than semi-crystalline PLA with the melting point at 160-170° C.

In Table 1, Fibers 1, 2 and 3 all have semi-crystalline PLA polymer as the core and amorphous PLA polymer as the sheath. In these fibers, the core provides the stiffness and strength, and the sheath component absorbs water and can rapidly degrade at given temperatures. Fiber 1 has reactive fillers in the core only, and loading of the filler is up to 10% of the core polymer (FIG. 3). For Fiber 2, reactive fillers (e.g., up to 10%) are also added into the sheath component and Fiber 3 has reactive fillers only in the sheath component (e.g., up to 10%). The weight % of sheath component in Fibers 1, 2 and 3 may be around 50-90%.

The configuration of Fibers 4, 5 and 6 is reversed with amorphous PLA as the core and semi-crystalline PLA as the sheath, but the components are otherwise the same as that of Fibers 1, 2 and 3. The configuration of Fibers 4, 5 and 6 allows the fibers to maintain stiffness and flocculation (fiber network in water to support proppant) for longer time and only break down at the later stage of degradation. The core component in Fibers 4, 5 and 6 may contain up to 10% reactive fillers, or the sheath up to 10%, or both. The weight % of the sheath component in Fibers 4, 5 and 6 may be around 10-50%, or be the same as above depending on the desired characteristics.

TABLE 1 Examples of polymers and fillers in degrable core-sheath PLA fibers Melt Melt point (° C.) point (° C.) Fiber Sheath Sheath ZnO in Core Core ZnO in ID polymer polymer Sheath Polymer polymer Core 1 6060D 125-135 no 6201D 160-170 yes 2 6060D 125-135 yes 6201D 160-170 yes 3 6060D 125-135 yes 6201D 160-170 no 4 6201D 160-170 no 6060D 125-135 yes 5 6201D 160-170 yes 6060D 125-135 yes 6 6201D 160-170 yes 6060D 125-135 no

Though the above examples of multicomponent composite fibers have core-sheath configurations, the arrangement of PLA components and the distribution of reactive fillers can be applied to island-sea configurations, side-by-side configurations and other configurations, such as braided or twisted.

Tables 2 and 3 show additional examples, where the configuration of the components is in an island sea configuration (Table 2), or a side-by-side configuration (Table 3). Segmented pie configuration and combinations of configurations are also possible. All the PLA polymers in Tables 1, 2, 3 and 4 have a Glass Transition Temperature (T_(g)) in the range of 55-60° C.

TABLE 2 Examples of polymers and fillers in degradable island-sea PLA fibers Sea Melting point Island ZnO compo- (° C.) Sea ZnO in compo- Melting point (° C.) in nent polymer Sea nent island polymer island 6060D 125-135 no 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 no 6201D 160-170 no 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 no

TABLE 3 Examples of polymers and fillers in degradable side-by-side PLA fibers Major Melting ZnO in Minor Melting ZnO in side point (° C.) major side point (° C.) minor polymer major side side polymer minor side side 6060D 125-135 no 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 no 6201D 160-170 no 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 yes 6201D 160-170 yes 6060D 125-135 no

As another alternative, the degradable polymers may be used to construct the sheath and the water soluble polymers may be used as the core (FIG. 4A). In this case, the hydrophobic, degradable polymeric sheath provides a layer of protection from moisture for longer shelf life, and the water soluble core provides mechanical strength to the fibers that should help to maintain the performance properties including proppant settling, bridging and plugging. When the fibers are exposed to water, the core with fast dissolution kinetics will dissolve first to result in a hollow degradable fiber with very thin wall (≦2 nm) which then degrades or even breaks down to small particles in the down-hole high pressure environment.

In yet another approach, we take advantage of fast physical dissolution of one component in the multicomponent fibers, where the other component will provide the stiffness, physical properties and easy processing. The water soluble polymers may be used to form sheath, sea, or one side of the multicomponent fibers, and degradable polyesters may be used to form core, island or the other side of the multicomponent fibers (FIG. 4B). In this case, the degradable polymers as the core provide the mechanical strength, stiffness, and process-ability for the multicomponent fibers, and the water soluble polymer as the sheath dissolves rapidly in water at ULT, which effectively reduces the degradable portion to only 10-50% of total weight.

In both cases, the water soluble polymers may occupy 50-90% of the fibers in order to take the most advantage of their fast dissolution kinetics at ULT. For example, the PVOH/PLA bicomponent fiber made herein takes much less time to reach the same weight loss % at the same degradation time and temperature compared to the degradation of a monocomponent PLA fiber, because the degradable polymer with slow degradation kinetics (several weeks to degrade) only accounts for 10-50% of the total weight of the fibers and the water soluble polymer with fast dissolution kinetics (several hours to dissolve) accounts for the major component of the multicomponent fiber.

Polyethylene oxide, polyvinyl alcohol (GOHSENOL, GOHSENAL, ECOMATY, and EXCEVAL from Kuraray), modified polyvinyl alcohol (Nichigo G-polymer from Nippon Gohsei), aliphatic polyamide (NP2068 of H. B. Fuller), sulfonated polyester (AQ38 and AQ55, Eastman), and polyacrylic ester/acrylic or methacrylic acid copolymers and blends thereof are examples of polymers for the water soluble component.

Poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(caprolacton) (PCL), polybutylene succinate polymers and polybutylene succinate-co-adipate polymers and copolymer or blends thereof are examples of polymers for the degradable polyester components.

The specific choice of the water soluble polymer for constructing the multicomponent fibers is based on the application temperatures. For example, if the wellbore temperature is at 38° C. or lower, AQ 38 or Nichago G-polymer may be used as one of the components in a bicomponent fiber.

Reactive fillers and other additives that can accelerate degradation may be placed in the degradable polyesters to improve the degradation of the polyester, and the loading is up to 10% (FIG. 4C). However, placing reactive fillers in water soluble polymers may provide a caustic aqueous environment that may facilitate rapid degradation of the polyesters (FIG. 4D).

Another approach is to construct multicomponent fibers in which the first polymer component provides stiffness and strength, where the second polymer dissolves in hydrocarbons at low temperatures (FIG. 5A-B). The first polymer in the fibers will partially degrade in water first during the stages of hydraulic fracturing, and the second polymer will dissolve in hydrocarbons during the production stage. The first degradable polymer could occupy the sheath, the sea or one side of a bicomponent fiber, and the hydrocarbon soluble polymer occupies the core, the island or the other side of a bicomponent fiber.

Polyolefins (such as polyprolylene PP or polyethylene PE), ethylene vinyl acetate (EVA), modified EVA and copolymers and blends thereof are good choices for the hydrocarbon soluble polymers, and specific selection of the polymer depends on the application temperatures. For this purpose, the water degradable composite may form the sheath (core-sheath), sea (island-sea), minor side (side-by-side), and the hydrocarbon soluble polymers form the core, island and the major side of the multicomponent fibers.

The weight ratio of water degradable composite and hydrocarbon soluble polymers is in the range of 10:90 to 90:10 depending on the desired resulting physical properties (stiffness and tensile) of the fibers and the application temperatures.

Fillers increase the porosity of the fibers, and can also facilitate faster dissolution. The loading of the fillers inside any of the fibers herein described also depends on the desired physical properties of the fibers (inorganic fillers reduce the tensile strength of the fibers). The process-ability of spinning composite fibers (fibers with inorganic fillers) also puts constraints on the loading of the fillers.

We expect to use no more than 10% weight percent of fillers inside the fibers. Some adhesion-promoting monomer or reactive functional polymers may be needed for better compatibility between the polymer matrix and the inorganic fillers. The choice of adhesion-promoting monomers includes silane based adhesion promoters (Silquest® brand, for example), maleated or acid functionalized polymers (DuPont Fusabond®, and Optim® E-117), and alkyl phosphate esters (Zelec® brand, for example). The choice of the adhesion promoters is determined by the choice of the fillers, and the loading of the adhesion promoters is the range of 0.5-5% of the total polymers.

In all the above fiber designs, small amounts of other additives or polymers such as compatibilizers, plasticizers, fire retardants, anti-microbials, pigments, colorants, lubricants, UV stabilizers, dispersants, nucleation agents, etc. that are commonly used in the plastic processing industry can be added to modify the fiber's characteristics and process capability. These additives include organic carboxylic acid, carboxylic acid ester, metal salts of organic carboxylic acid, multicarboxylic acid, fatty acid esters, metal salts of fatty acid, fatty acid esters, fatty acid ethers, fatty acid amides, sulfonamides, polysiloxanes, organophosphorous compound, Al(OH)₃, quaternary ammonium compounds, silver base inorganic agents, carbon black, metal oxide pigments, dyes, silanes, titanate etc.

Although the degradation of the multicomponent fibers shown herein were conducted in water or in buffer solutions, this application does not preclude the use of other external, pH adjusting additives in the solution to further accelerate the rate of degradation of multicomponent fibers. As an example, thus use of pH changers to initiate rapid degradation downhole may be used.

PLA/PLA Samples

Table 4 shows the spinning conditions and Table 5 shows the composition and tensile strength of the sheath-core bicomponent fibers that were actually made. The amorphous PLA 6060D occupied the sheath component that facilitated fast water absorption and degradation, and the crystalline 6201D resin occupied the core that provided stiffness and strength.

TABLE 4 The extruder zone temperatures for the bicomponent PLA fibers Take Zone Temperature (° C.) Total up Spinneret inside extruder throughput speed temperature Zone 1 Zone 2 Zone 3 Zone 4 (ghm) (m/m) (C.) Bi—75S/25C, Bi—50S/ Sheath (6060D) 180 185 195 205 0.2315 960 250 50C Core (6201D) 205 220 232 245 Bi—50S/50C—ZnO Sheath (6060D) 180 185 195 205 0.2701 700 250 Core (6201D) 200 215 225 235

The samples are named according to their type (e.g., Bi for bicomponent) and sheath/core ratio (e.g., 50S/50C is 50% of each), and finally reactive filler is indicated at the end. Thus, Bi-75S/25C is 75% sheath surrounding a 25% core, and Bi-50S/50C—ZnO is 50/50 sheath/core with ZnO added, in this case to the core.

The crystallinity % of Bi-50S/50C was higher than that of Bi-75S/25C since the percentage of the crystalline polymer in the core was higher. Consequently, the T_(g) and the tensile strength of the fibers with higher % crystallinity were also higher. Bi-50/50-ZnO has 4% of ZnO fillers in the core component only, and this fiber's tensile strength, T_(g) and crystallinity were lower than that of the ZnO-free Bi-50S/50C. These results indicate possible polymer degradation during the fiber spinning process. FIG. 6 shows the photomicrographs of the bicomponent fibers.

TABLE 5 The characteristics of the bicomponent fibers Fiber Tensile Elongation Sheath % Core % ZnO % in diameter strength at Break T_(g) % crystallinity in ID (S/C ratio) (6060D) (6201D) Core (μm) (Mpa) (%) (° C.) total fiber Bi-75S/25C 75% 25% 0 18 ± 1.3 261 ± 32 61 ± 14 62.11 11.83 Bi-50S/50C 50% 50% 0 16 ± 1.0 313 ± 17 75 ± 8  63.47 21.60 Bi-50S/50C—ZnO 50% 50% 4% 25 ± 3   169 ± 45 87 ± 58 59.31 18.81

The PLA bicomponent fibers were cut to 6 mm long. A fixed amount of the fibers was immersed in 100 ml of DI water. The bottles were kept at 60° C. for 7, 14 and 21 days. After degradation, the residuals were filtered and washed with DI water three times before being dried at 49° C. in an oven. The weight loss as a percentage of the total original weight was calculated and used as the degree of degradation. See FIGS. 7 and 8.

As shown in FIG. 7, Bi-75S/25C fiber with more amorphous PLA 6060D had more weight loss % than the Bi-50S/50C fiber with less amorphous PLA. The addition of 4% reactive filler, ZnO, in the core resulted in more weight loss % for Bi-50S/50C—ZnO compared to the similar fiber Bi-50S/50C at the same degradation condition (FIG. 8).

We also added a variety of additives to the water to determine their effects on degradation. The PLA fibers were provided by NatureWorks. A fixed amount (1.2 mg) of PLA fibers were dispersed in 100 ml of DI water. 50 mmol of water insoluble additive was added to the mixture. The mixture was placed in the oven at 66° C. for 48 h. After that time, the mixture was cooled down to room temperature, the residues were filtered off, washed with 6% HCl and DI water, dried at 50° C., and weight determined. The results are shown in FIG. 9, where it can be seen that all additives increased the degree of degradation at 48 hours, especially the combination of ZnO and 4-dimethylaminopyridine. However, PLA containing both ZnO 4-dimethylaminopyridine only showed slightly higher degradation compared with PLA containing only ZnO fillers. Although compared to ZnO, MgO is more effective to accelerate PLA degradation, the melt spinning of PLA fibers with MgO as a filler turned out be very challenge even at very low weight % of MgO (<1%). The spinning was interrupted frequently due to fiber breakage.

PLA/G-PVOH Samples

Nichigo G-Polymer™ (referred to as G-PVOH in this patent), developed by Nippon Gohsei, is a hydrolyzed copolymer of vinyl acetate and proprietary comonomers. G-PVOH is an amorphous polymer that combines ordinarily conflicting traits of “low crystallinity” and “high hydrogen-bonding strength,” and realizes functions of water solubility at room temperature, low melting points, high stretching characteristics, and a wide temperature gap between the melting point (185° C.) and the thermal decomposition temperature (>220° C.) which make it possible to develop fibers and films using conventional melt extrusion processes.

Nichigo G-Polymer™ 8042 P (MFI 28 g/10 min, Tm=173° C., SAP value 88-90% mole %) or 8070P (MFI 17 g/10 min, Tm=170° C., SAP value 88-90% mole %) was used to make the exemplary bicomponent PLA/G-PVOH fiber. NatureWorks amorphous PLA 6060D resin was used to construct the sheath (≦30%), and 8042P was used to construct the core (≧70%) of the bicomponent fiber.

The melt spinning of PLA/G-PVOH bicomponent fibers was conducted on a Hills Bicomponent Pilot Machine in the Fiber Science Lab of Nonwovens Institute. The spinning conditions are outlined in Table 6:

TABLE 6 the spinning conditions of the PLA/G-PVOH bicomponent fiber. Zone Temperature (° C.) Total Sheath/Core inside extruder Spinning throughput Speed ratio Zone 1 Zone 2 Zone 3 Zone 4 temperature (° C.) (ghm) (m/m) Sheath (6060D) 30%/70% 170 190 220 230 235 0.74 1000 Core (G-8042P) 170 185 210 230

The SEM image shows the as-spun PLA/G-PVOH fiber (FIG. 10A), and the optical image of the cross-section of the fiber clearly indicates the big core surrounded by a thin layer of sheath polymer (FIG. 10B). The average fiber diameter was 27 μm and the thickness of the sheath was 3 μm with the spinning speed set at 1000 m/m.

The degradation of the PLA/G-PVOH bicomponent fiber was conducted in water at different pH (acid, DI water or base buffers) at 49° C. and 60° C. for 7, 14 and 21 days. The percentage of weight loss (weight loss %) was used to measure the degradation.

FIG. 11 shows the weight loss % vs. degradation time and temperature in various pH aqueous solution. At both temperatures (49° C. and 60° C.), the PLA/G-PVOH fibers lost more than 70% weight after only 7 days in DI water or at different buffer solutions (FIG. 11) and form hollow fibers with <2 μm thin wall at 49° C. (FIG. 12A) and the hollow fiber broke down at 60° C. (FIG. 12B). The pH of the solutions, in contrast, had little effect on the rate of degradation. The weight loss % is determined by the weight % of water soluble component in the fibers.

EVA Sample

One specific example of a hydrocarbon soluble polymer is ethylene vinyl acetate. Ethylene vinyl acetate (EVA) is the copolymer of ethylene and vinyl acetate. Commercial grades of EVA resins have vinyl content ranging from 9 to 40% and a melt flow index range from 0.3 to 500 dg/min. These specialty thermoplastic polymers are inherently flexible, resilient, and tough, and can be processed using conventional thermoplastic or rubber handling equipment and techniques.

The melt spinning process for fibers requires resin melt index in the range of 10 to 45 g/min (ASTM D1238, modified), and Melt Viscosity in the range of 10 to 20 (Pa S) at 190° C. temperature. The VA % (vinyl acetate content in the EVA copolymer) impacts the flexibility and the toughness of the resin and the final products. Higher VA % results in more flexible and tougher products.

The following EVA resins: DuPont Elvax® 550 and Elvax® 250, and Arkema Evatane® 20-20, 33-15, 28-05 and 28-40, were chosen for the initial trial based on their % of vinyl acetate content and their melt index (ASTM D1238), though EVA resins from other brands and suppliers should be equally useful.

Different grades of EVA polymers may be blended to make homogeneous or heterogeneous blend fibers for optimum process-ability and properties. The choice of the resins for EVA blends is determined by the melting point and the Ring and Ball Softening point of the resins. Blending of EVA resin with other resins for better physical properties of the resultant blend fibers is also under consideration. Polymers other than EVA may be blended with the EVA resin to improve the physical properties of the fibers. The choice of polymers includes polyolefins and polyolefin oligomers (ethylene or propylene), wax, pitch and bitumen.

The EVA resins also have good solubility in hydrocarbons at low temperatures. The solubility of the EVA resins was checked by the following experiment: 0.25 g of EVA resin completely dissolved in 8 ml of octane after 2-5 hours at 38° C. FIG. 13 shows the pictures of Evatane® 28-05 and Evatane® 28-40 resins dissolved in octane at 38° C. Although no actual multicomponent fibers are made yet, this result indicates that it is possible to make a fiber where one component is soluble in petroleum.

The preceding description has been presented with reference to some embodiments. Persons skilled in the art and technology to which this disclosure pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this application. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.

The statements made herein merely provide information related to the present disclosure and may not constitute prior art, and may describe some embodiments illustrating the invention. In particular, the following references may generally relate to certain subject matters of the current application and are hereby incorporated by reference to the current application in their entireties for all purposes:

-   Zhang X. et al., ‘Morphological behavior of poly(lactic acid) during     hydrolytic degradation’, Polymer Degradation and Stability 93 (2008)     1964-1970 and ref therein. -   Tarantili P. A., ‘Swelling and hydrolytic degradation of poly(D,     L-lactic acid) in aqueous solution’, Polymer Degradation and     Stability 91 (2006) 614-619 and ref therein. -   Xanthos Q., ‘Nanoclay and crystallinity effects on the hydrolytic     degradation of polylactides’, Polymer Degradation and Stability     93 (2008) 1450-1459 and ref therein. -   Ratheesh et al., Materials Chemistry and Physics 122 (2010) 317-320     (coating on MgO). -   Meyer B. et al., ‘Partial dissociation of water leads to stable     superstructures on the surface of ZnO’, Angew. Chem. Int. Ed. 2004,     43, 6642-6645. -   Chrisholm et al., ‘Hydrolytic stability of sulfonated poly(butylenes     terephthalate’, Polymer, 44 (2003) 1903-1910. -   Guido Grundmeier et al., ‘Stabilization and acidic dissolution     Mechanism of Single-Crystalline ZnO(0001) surfaces in electrolytes     studied by In-Situ AFM Imaging and Ex-Situ LEED’, Langmuir 2008, 24,     5350-5358. -   Martin Muhler, et al., ‘The identification of hydroxyl groups on ZnO     nanoparticles by Infrared spectroscopy’, Phys. Chem. Chem. Phys.,     2008, 10, 7092-7097. -   Arrigo Calzolari, et al., ‘Water adsorption on Nonpolar ZnO(1010)     surface: A microscopic understanding’, J. Phys. Chem. C, 2009, 113,     2896-2902. -   PCT/US11/49169, ‘Mechanisms for treating subterranean formations     with embedded additives’. -   US20120231690, US20120238173, US20060083917, US20100273685, U.S.     Pat. No. 5,916,678, U.S. Pat. No. 7,858,561, U.S. Pat. No.     7,833,950, U.S. Pat. No. 7,786,051, U.S. Pat. No. 7,775,278, U.S.     Pat. No. 7,748,452, U.S. Pat. No. 7,703,521, U.S. Pat. No.     7,565,929, U.S. Pat. No. 7,380,601, U.S. Pat. No. 7,380,600, U.S.     Pat. No. 7,275,596. 

1. A degradable multicomponent fiber, comprising: a) a degradable polymer selected from the group consisting of polylactic acid (PLA), polycarprolactone, polyglycolic acid, polylactic-co-polyglcolic acid, or a mixture thereof; b) a water soluble polymer or a hydrocarbon soluble polymer; and c) a reactive filler mixed with component a, that shortens the degradation time of said component when mixed therewith; d) wherein component a is different than component b; and e) said multicomponent fiber having a diameter of less than 100 micrometers, having a configuration selected from the group consisting of sheath-core, islands-in-the-sea, ribbon, segmented pie, side-by-side, and combinations thereof, and said fiber being degradable in 30 days or less at 60° C.
 2. The fiber of claim 1, said reactive filler being selected from the group consisting of Ca(OH)₂, Mg(OH)₂, CaCO₃, Borax, MgO, CaO, ZnO, NiO, CuO, and Al₂O₃.
 3. A degradable multicomponent fiber, comprising: a) a degradable polyester; b) a water soluble polymer or a hydrocarbon soluble polymer; c) a reactive filler that shortens the degradation time of component a, said reactive filler being selected from the group consisting of Ca(OH)₂, Mg(OH)₂, CaCO₃, Borax, MgO, CaO, ZnO, NiO, CuO, 4-Dimethylaminopyridine (DMAP), and Al₂O₃; d) wherein component a differs from component b, and wherein components a and b are adjacent each other in said fiber, and wherein said fiber degrades in ≦30 days at 60° C. in water.
 4. The fiber of claim 3, said degradable polyester selected from the group consisting of polylactic acid (PLA), polycarprolactone, polyglycolic acid (PGA), polylactic-co-polyglcolic acid (PLGA), and a mixture thereof.
 5. The fiber of claim 3, said hydrocarbon soluble polymer comprising ethylene vinyl acetate, olefin, propylene, ethylene, or combinations thereof.
 6. The fiber of claim 3, said water soluble polymer comprising polyvinyl alcohol, modified polyvinyl alcohol, or their mixtures.
 7. A multicomponent fiber comprising a first degradable polymer adjacent a second hydrocarbon soluble polymer, wherein said fiber degrades in water and petroleum.
 8. The fiber of claim 7, said degradable polymer comprising a polyester, polylactic acid (PLA), polycarprolactone, polyglycolic acid (PGA), polylactic-co-polyglcolic acid (PLGA), or a mixture thereof.
 9. The fiber of claim 7, said degradable hydrocarbon soluble polymer comprising ethylene vinyl acetate, olefin, propylene, ethylene, or combinations thereof.
 10. The fiber of claim 7, said further comprising a reactive filler mixed with said polyester to accelerate its degradation rate, and said reactive filler is Ca(OH)₂, Mg(OH)₂, CaCO₃, Borax, MgO, CaO, ZnO, NiO, CuO, Al₂O₃, DMAP, or mixtures thereof.
 11. The fiber of claim 7, said further comprising a ZnO mixed with a PLA.
 12. A multicomponent fiber comprising an amorphous PLA adjacent a crystalline PLA and ZnO intimately admixed with either or both, said fiber having a diameter of less than 100 μm and being degradable in water at 60° C. in 30 days or less.
 13. (canceled)
 14. (canceled)
 15. A method of producing hydrocarbon from a subterranean reservoir, comprising: a) injected a fluid comprising water and a fiber of claim 1 into a subterranean reservoir comprising a hydrocarbon; and b) producing said hydrocarbon. 